A molecule composed of a disk-shaped, rigid, essentially planar core to which four or more flexible aliphatic chains or tails are attached forms the basic structure inherent to the discotic mesogen. This disk-like anisotropy of molecular shape leads to the discotic mesophase wherein the disk-like molecules organize together into thermotropic liquid crystalline columnar structures. By way of contrast, the more commonly encountered rodlike anisotropy of molecular shape, does not lead to the discotic mesophase. According to S. Chandrasekhar and G. S. Ranganath, Rep. Prog. Phys., 53(1), 57 (1989), discotic liquid crystallinity is generally classified into two structural categories: "The columnar phase, in its simplest form, has long-range translational periodicity in two dimensions and liquid-like disorder in the third, whereas the nematic phase is an orientationally ordered arrangement of discs without any long-range translational order." The discotic nematic phase contrasts to the nematic phase exhibited by numerous rodlike mesogenic molecules in that the director represents the preferred orientation of the short molecular axis versus the long molecular axis for rodlike mesogenic molecules. Some variation on the flat, planar core structure of the discotic mesogen can be tolerated while still preserving the columnar mesophase. For example, G. Cometti, E. Dalcanale and A. Du Vosel, Liquid Crystals, 11(1), 93-100 (1992) have prepared bowl-shaped molecules which exhibit a columnar liquid crystalline phase. Similarly, J. Malthete and A. Collet, Nouve. J. Chem., 9, 151 (1985) have replaced the flat, planar core structure with a conical one providing molecules which still exhibit a columnar mesophase. The presence of the flexible aliphatic chains or tails attached to the disk-shaped core is critical to achieving the discotic liquid crystalline state. Chemical structure, length and presence of branching are some of the variables relating to the aliphatic chains that are frequently manipulated to modify discotic mesophase structure and behavior. Regarding the number of flexible aliphatic chains that are required to achieve the discotic liquid crystalline state, it is fully recognized that certain exceptional molecules exist, such as the 1,7,13-trialkanoyldecacyclenes prepared and characterized by E. Keinan, S. Kumar, R. Moshenberg, R. Ghirlando and E. Wachtel, Adv. Mater., 3, 251 (1991) and the 1,3,5-tri(4-alkoxyphenoxycarbonyl)benzenes (the hexyloxy and decyloxy homologs) prepared and characterized by S. Takenaka, K. Nishimura and S. Kusabayashi, Mol. Cryst. Liq. Cryst., 111, 227-236 (1984). Thus the discotic liquid crystalline state depends upon the intermolecular attraction between the disk-like core structures leading to molecular stacking coupled with hydrophobic interaction between aliphatic chains which precludes long range three dimensional order. Thus for the 1,7,13-trialkanoyldecacyclenes the presence of the large polycyclic aromatic core maximizes attractive core to core interactions and thus appears to reduce the requirement for hydrophobic interaction between the aliphatic chains required for the discotic mesophase to be achieved. For the 1,3,5-tri(4-alkoxyphenoxycarbonyl)benzenes (the hexyloxy and decyloxy homologs), interaction of the 4-alkoxyphenoxycarbonyl groups induces molecular symmetry as determined by conformational isomerization around the ester plus increased polarizability due to the alkoxy groups and thus appears to reduce intermolecular attraction between the disk-like core structures required for the discotic mesophase to be achieved.
For molecules such as triglycidyloxynaphthalenes, specifically, 1,3,6-triglycidyloxynaphthalene, disclosed in Japanese Patent No. 1-268,715-A; the triglycidyl ether of trihydroxybiphenyl, tetraglycidylbenzophenone, and the tetraglycidyl ether of bisresorcinol, disclosed in U.S. Pat. No. 5,037,934; 1,3,5-triglycidyloxybenzene, disclosed in U.S. Pat. No. 4,992,488; 3,3',5-triglycidyloxybiphenyl disclosed in U.S. Pat. No. 4,954,583; the diglycidyl ethers of tetra-C.sub.1-12 hydrocarbyl group substituted dihydroxybenzenes, disclosed in WO 86/03507; the diglycidyl ethers of tetra-C.sub.1-10 hydrocarbyl or hydrocarbyloxy group substituted dihydroxybenzenes, disclosed in U.S. Pat. No. 5,164,464; or the monoepoxyhexahydrobenzyl (mono-, di-, or tri-glycidyloxy substituted)benzoates disclosed in SU 591,471 discotic liquid crystallinity is not reported nor expected. In the relationship between the core to core interactions and the hydrophobic interaction between the aliphatic chains required for the discotic mesophase to be achieved, a certain minimum constraint in the size and other variables of the aromatic core and in the number, structure (size, type, etc.) of aliphatic chains exists. Thus, the benzene, naphthalene, biphenyl or benzophenone groups of the aforementioned compounds possess inadequate core to core attractive interactions in combination with inadequate hydrophobic interactions between the aliphatic chains (glycidyl groups, hydrocarbyl groups, etc.) substituted therein to be discotic mesogens.
Diglycidyl ethers of bis(anthrols) and bis(naphthols) of the following formulas are known from U.S. Pat. No. 4,908,424: ##STR1## wherein each X.sup.1 and X.sup.2 is independently an alkyl group containing 1 to 4 carbon atoms or a halogen atom having an atomic number of from 9 to 35, inclusive; m is 0, 1 or 2; n is 0, 1, 2, 3 or 4; and A is a divalent hydrocarbon radical selected from the group consisting of and alkylene group containing from 3 to 8 carbon atoms, or a radical derived from a non-aromatic carbocyclic group or a dialkyl aromatic or non-aromatic carbocyclic group containing from 7 to 24 carbon atoms in which each alkyl group contains from 1 to 8 carbon atoms and the carbocyclic group comprises a central non-aromatic ring containing 5 to 7 carbon atoms in a ring or a central aromatic carbocyclic ring, each central ring optionally bridged or fused with a non-aromatic or aromatic carbocyclic ring. When A is a dialkyl aromatic or non-aromatic carbocyclic group, it should be understood that the bonds from A to the anthrol or naphthol group are from the alkyl substitutents of the dialkyl carbocyclic group. Discotic liquid crystallinity is not reported nor expected for these compounds. Specifically, diglycidyl .alpha.,.alpha.'-bis(10-anthr-9-one)-p-diisopropylbenzene with a melting point of 160-170 deg. C. and the diglycidyl ether of .alpha.,.alpha.'-bis(1-hydroxy-2-naphthyl)-p-diisopropylbenzene with a melting point of 167-168 deg. C. were prepared and polymerized with a variety of phenolic and amine curing agents. Discotic liquid crystallinity is not reported for either of these compounds nor the polymerized compositions thereof.
Liquid crystalline polymers containing disk-like mesogens both in the main chain of the polymer backbone and as side chains have been prepared. For example, W. Kreuder and H. Ringsdorf, Makromol. Chem., Rapid Commun., 4, 807-815 (1983) prepared discotic polysiloxanes containing pentaalkyloxysubstituted triphenylene moieties attached as side chains to the polymer backbone via flexible spacers. Similarly, W. Kreuder, H. Ringsdorf and P. Tschirner, Makromol. Chem., Rapid Commun., 6, 367-373 (1985) prepared discotic polyesters containing tetraalkyloxysubstituted triphenylene moieties incorporated into the main chains of the polymer backbone. Both classes of polymers exhibited discotic liquid crystalline behavior. Virtually all of the discotic liquid crystalline polymers known to date are thermoplastic.
The present invention provides the heretofore unknown classes of thermosettable epoxy, polythiirane and vinyl ester resin compositions containing one or more discotic mesogenic moieties. Said resins exhibit unique molecular order in the melt phase as a result of the discotic mesogenic moieties contained therein. Surprisingly, in certain compositions of the present invention, the flexible aliphatic chains or tails required for discotic liquid crystallinity can be completely replaced by thermosettable glycidyl ether moieties, while still maintaining discotic liquid crystallinity. The discotic liquid crystalline morphology can result in enhanced physical and mechanical properties, such as, for example, increased strength and thermal stability.
The term "discotic mesogenic moiety" or "discotic mesogen" is used herein to describe a molecule composed of a disk-shaped, rigid, essentially planar core to which flexible aliphatic chains or tails may be attached. Said flexible aliphatic chains or tails are attached via functional groups present in the discotic mesogenic moiety. Furthermore, the vicinal epoxide group, the vicinal thiirane group and the vinyl ester (prepared via reaction of the epoxide group and a polymerizable ethylenically monounsaturated monocarboxylic acid) group are all considered as members of the group of flexible aliphatic chains or tails.